Expert opinions needed on metal detector usage for medical diagnostic purposes

[jake_r]

Hello folks,

I have no prior experience with metal detecting and not sure exactly what forum this post should be in, so please feel free to redirect me if you know a better place to post this question.

I am a doctor with the US military and interested in leveraging (handheld) metal dectors for the purposes of detecting and localizing embedded shrapnel and metal fragments in the human body. There has been a good deal of success with doctors using handheld metal detectors to detect foreign metal within the human body as evidenced by this whitepaper http://www.medscape.com/viewarticle/509541_print. These techniques offer a fast and cost-effective way to detect foreign metal in the human body as opposed to the traditional radiology route. Detection/verification of ingested coins in childrens' GI tracts is one good example. Several of these studies appeared to use the Garret Super Scanner handheld metal detector, however I am not convinced that this is necessarily the best detector for this context.

I would like to detect metal fragments that may be much smaller than a coin, and therefore would like to enlist your experienced opinions on what technology/model may work best for me. My constraints follow:

1) Discrimination of metal types is not important. Since all metal would be foreign to the human body, I would like to be made aware of any metal of any size.
2) Metal fragments I would like to detect might be as small as 6mm x 2mm metal cylinder.
3) Fragment depth is usually about 1 inch. I don't anticipate ever needing more than 4 inches depth.
4) Ideally I'd be able to use a "pinpointer probe" style wand detector or handheld device (more portable than a full blown rod/coil setup), however if a larger device was required, then it is what it is.
5) Detection of small pieces of metal is more important than accurate or exact localization of the pieces. Once fragments in a certain area are confirmed, we can use radiology at that point for exact imaging.

6) The conductivity of the human body may be a factor. Assume the human body has a conductivity around 1.0 S*m^-1. In comparison, aluminum metal has a conductivity about 37,800,000 S*m^-1, seawater averages about 5.0 S*m^-1, drinking water is 0.05 S*m^-1. Conductivity of soil depends on water, salt, and mineral content but generally falls between 0.25 S*m^-1 to 0 (zero) S*m^-1.

In other words, the human body is about 1/5 of the conductivity of seawater (saltwater) but is still significantly more conductive than even wet ground.

With all this in mind, does anyone have any opinions on the best suited technology for these purposes? PI seems attractive since it won't be affected by the conductivity but I am worried about its sensitivity in detecting small metal fragments as described above. Would higher freq VLF be an option (higher freq to detect small pieces?)

Some detectors I have been looking at are on this page http://www.metaldetector.cc/index.asp?PageAction=VIEWCATS&Category=22 .

For example, maybe the PI-utilitizing DetectorPro Pocket UniProbe? But my fear is that it wouldn't detect a small 6mm * 2mm sized fragment. Are these fears unfounded? Any advice would be appreciated..

Thanks,
Jake R

 

[cosmic]

I suggest contacting the manufacturers.. But I believe the PI would be ideal.. Also it shouldn't have a problem with that sized objects..

 

[SteveP(NH)]

I think that a Uniprobe or PistolProbe (made my the same company DetectorPro but small with more compact electronics) would work well for the medical application you describe.

I use a Garrett ProPointer so I just did a test to see how well it would work even though the ProPointer is generally acknowledged to not be as sensitive as the DetectorPro pinpointers. My test piece of metal was an old fired 22 bullet that I dug up about a month ago. The bullet apparently had not struck anything as it still retained its cylindrical shape. It measured (using callipers) 3 mm * 6 mm. I believe it to be made of lead based on the target ID of my Teknetics T2 detector.

I placed the bullet on a flat wooden surface with no other metal in it then placed my hand over the bullet and detected the bullet through my hand. Since my hand gradually gets thicker as I positioned it so that the bullet was detected through the part closer to my wrist I was able to get what I think is a pretty precise reading of how much tissue and bone the Garrett Propointer would detect it through.

My results were that the Garrett can readily detect that sized bullet through about 30 mm or 1 and 3/8th inches of tissue and bone. Based on the online claims I've seen of the depth that the DetectorPro probes are capable of, it seems likely that one could expect approximately double the depth I got using the Garrett probe. Perhaps someone who owns a Uniprobe or the new PistolProbe could do a similar test.

 

[bbsailor]

Jake R,

I am a retired Federal Civil Service person out of CECOM so I can well appreciate the red tape you must go through to obtain a Pulse Induction Probe that could localize metal fragments in the body.

Here is a web link that sells soft ferrite rods http://www.surplussales.com/Inductors/FerRods/FerRods.html . I have successfully used the 7.5mm X 50mm made of 3C80 ferrite.

Wrap this ferrite rod with a 1.5" long layer plus another 0.75" layer of AWG 30 single strand Teflon insulated wire making about a 325 uH inductor. By connecting this to my CS6PI commercial metal detector in place of the mono standard coil, I am able to detect small metal objects a few inches away. You may want to ground the ferrite rod by using rubber grommets as the ends to make a bobbin to hold the wire and the slip a flat desoldering wick under the rubber grommet to ground the ferrite to minimize noise. To further reduce noise you might want to obtain Scotch 24 wire mesh shielding and put one single layer of this mesh around the probe, over the wire with the ends not touching around the circumference, to prevent eddy currents from being developed. Ground this Scotch24 shielding mesh to the ferrite core ground wire and one coil wire and you will have an inexpensive and effective probe. If you want a little more depth, glue two probes together making about a 4" long probe and wind one layer of wire or until you have about 325uh of inductance and that will extend the probe reach a little more. If you use this probe in place of a mono coil on a high power PI machine you will need to put about a 10 to 20 ohm (1 watt) resistor in series with the coil to keep the ferrite from saturating. Wedge some foam around the resistor to keep it from moving and giving a false signal. You can mount this whole assembly in a short length of common household 0.5" ID plastic water pipe with a nipple on each end.

This is my free gift back to the Government. Maybe it will save some lives. Send me a private e-mail and I'll give you more details. bbsailor@aol.com

bbsailor

 

[jake_r]

Thank you all for your valuable insight and taking the time to reply. I am excited to run some trials and see how theses technologies work out.

Thanks again,
Jake

 

[;hgarr]

I believe the Detector Pro pocket probe would do a good job on this large a target. About the smallest gold nugget it will pickup is a flattened slightly 2 to0 3 grain size which is about 1/8 inch circular by about 1/16 inch thick.which it will pickup about 1/2 inch deep in black sand. I believe it would pick up your sample of .234 x .078 about 4 inches through flesh and bone if using earphones and a little experience using it. The thing that bothers me is that I don't remember the length of the field from the tip, maybe two or three inches, therefore requiring a number of sweeps to find the tiny shrapnel. A White's Electronics GMT gold nugget detector would work really well, but would require the 4x6 inch Shooter coil on a handle instead of on a shaft. You could then ground balance to someone's hand or arm once and then be able to use it on anyone thereafter. The GMT, though, would not be as easy to use as the pocket probe. I hope this might be of help in your studies........best of luck.....How.
t

 

[puncher]

Hi Jake
Try Wizard Probes, thats what they are made for, it has a light on the probe and it either buzzers or vibrates when encounters a metal object and they are cheap and they are used in forensics.
Hope this helps , good luck
puncher

 

[Joel-Winnipeg]

Im not an expert in any of the above diciplines but have no problen detecting small staples in the soil.
The new Garrett pin pointer will pick my teeth fillings when placed against my jaw. One of the ways I test pinpointers that I'll buy.

 

[AUDuke]

I vote for the uni probe

 

[;hgarr]

There are the security paddle detectors used at airports and large buildings that should be sensitive enough to find small embedded shrapnel in the depths necessary for good, fast body surveillance purposes. White's, Garret's and others manufacturers make these security paddle shaped detectors. Please let us know how your tests work out,,,,,,Best of luck....How.

 

[bearkat4160]

I wouldnt recommend a PI if you are planning on using it indoors, unless it is maybe a PI pinpointer. A good inexpensive detector that has an all metal mode and can be detatched from shaft for ease of use is what i would use. Like a Tesoro Vaqeuro or Garrett Scorpion, both operate around 15k.

Alan

 

[Dave J.]

Excellent Medscape article, Jake. Thanks for the link. In my spare time I'll have to check out some of their other medical research info.

"Pinpointers" whether PI or CW, may not have the combination of depth and small-target sensitivity to find metal objects which are both small and deep, esp. if of a low conductivity alloy such as stainless steel.

Most "security wands" deliberately have low sensitivity and will not find the small metal fragments you are interested in. The company I work for recently introduced a high-sensitivity "wand" for use in the cabinetmaking and lumber industry which might do the job: if you're interested send me a private email and we can take it from there.

What will do the job is a high-sensitivity hobby-type so-called "VLF induction balance" metal detector with an operating frequency preferably above 10 kHz, preferably designed with gold prospecting in mind either as a primary or secondary use, and equipped with a small searchcoil. Unfortunately most of these are big awkward things (in a medical setting). There are a few which can be dismounted from the pole and used as bench units. Since this is a matter which others here are knowledgeable enough to comment on, I'll stay out of the "which make and model" discussion unless specifically invited into it. Such a discussion (since it's not specific to PI) might get moved to another more appropriate forum.

With such a VLF-IB metal detector, you'll run into at least 4 problems, which aren't "killers" but you need to be aware of them.

1. You'll get pickup from all those large masses of metal in the immediate vicinity, as you move the searchcoil around. You'll have to turn down the sensitivity, and mentally "listen through" the sound from that metal.

2. You'll get pickup from the conductivity of the human body. You'll probably have to turn down the sensitivity, and mentally "listen through" the sound that remains.

3. There will probably be lots of electrical interference from medical apparatus, flourescent lamps, computer systems, telephone exchange lines, electronic thermostats, etc. You'll have to turn down sensitivity, and on machines which provide the option to shift frequency, you'll have to try that as well. You may have to turn off offending interference sources temporarily while using the the metal detector.

4. A metal detector with the capability of doing the job requires some knowledge to operate properly so you'll get the best results from it.

A detector which is less sensitive to begin with is not the optimum solution to the problem, because those usually operate at lower frequencies and usually don't have a true all-metals operating mode.

Although PI machines will usually ignore human body electrical conductivity, they tend to be more susceptible to electrical interference. The ones designed for detecting gold should have adequate small-target sensitivity; others may not. For your application you don't need ground balancing. .........Although in principle a PI could be built which would be overall as useful in this application as a VLF-IB (while having somewhat different characteristics), when it comes to PI's there's not a lot to choose from, and I can't think of any models which would likely do as well in your application as a good VLF. There..... now that I've said that, and since this is the PI forum, someone will probably suggest a promising model, and then you'll have more to choose from.

--Dave J.

 

[Eric Foster]

Hi Dave,

Good to see you posting here. The link below is of a PI detector that I designed some years ago for the clothing industry. It has a 3uS TX pulse and a 1uS delay, and will pick up very tiny bits of metal. It runs from a small wall socket power supply. As you say, the treasure hunting probes would not normally have the sensitivity required for this application.

http://www.eriez.com/Products/MetalDetectorsIndustrial/MetalarmMetalDetector/hhmd/

Eric.

 

[Uncle Willy]

The new Garrett Pro-Pointer operates at maximum sensitivity in all metal at 12 khz and is sensitive to small objects such as tiny gold nuggets or BB's. Since Garrett is the largest manufacturer and supplier of security detectors if the PP didn't work as his for his needs perhaps the engineers could modify one to fit his needs.

Bill